Odontomas
are classified by the WHO as odontogenic tumors composed of enamel,
dentin, cement and pulp, considered hamartomatous lesions rather than
true neoplasms. In exceptional cases, odontomas erupt into the oral
cavity.

This study reports a case of
odontoma spontaneously exposed to the oral cavity, which is known as
“erupted odontoma”, in a 22-year-old male patient. A review of the
literature between 1980 and 2015 of the existing cases of this
pathology is also presented.

Keywords: Odontogenic tumors, odontomas, Erupted odontoma.

Received on: 16 Jun 16 – Accepted on: 30 Aug 16

Introduction

Maxillary tumors of odontogenic origin are lesions that occur only on both jaws and that arise from odontogenic tissue.

They
have clinical and histological peculiarities. In its 2005
classification, the WHO divides odontogenic tumors into three groups:
odontogenic epithelial tumors with mature stroma without odontogenic
ectomesenchyme, odontogenic epithelial tumors with ectomesenchyme with
or without hard tissue formation, and tumors with mesenchyme and/or
ectomesenchyme with or without odontogenic epithelium.

Odontomas
fall into the third category and are considered benign malformations
(hamartomas) composed by dental tissue and ectomesenchymal cells (1,
2).

Background

Broca was the first person who used the term odontoma
in 1867 in a broad sense to refer to any tumor of odontogenic origin.
Although the WHO classifies them as benign odontogenic tumors,
odontomas are considered hamartomas or development defects rather than
true neoplasms (1). They are the most frequent non-cystic odontogenic
lesions and account for between 22 % and 67 % of all odontogenic tumors
(3).

Odontomas are formed by enamel,
dentin, cementum and pulp, and are classified into compound odontomas
and complex odontomas. There are also mixed lesions (compound-complex
odontomas). Compound odontomas (CpOD) display dental tissues in an
organized manner and might present tooth-like structures known as
denticles. Complex odontomas (CxOD) present all dental tissues but they
are haphazardly arranged(2, 4, 5).

Clinically,
odontomas can be classified into central (intraosseous), peripheral
(extraosseous), and erupted (6). Central odontomas are the most
frequent odontogenic tumors. Peripheral odontomas occur only in the
soft tissue covering the mandible and maxilla. Erupted odontomas are
intraosseous odontomas that appear exceptionally in the oral cavity
through processes discussed below.

Odontomas
grow slowly, are usually asymptomatic, and occur most frequently in the
maxilla. They are usually detected during the first two decades of
life, within an age range of 6 to 46. Shafer reports an average age of
23 and no sex predilection (7).

They
are often detected on routine radiographies or when lack of eruption or
delayed eruption is investigated. Most are linked to tooth
malformation, impaction, malposition or delayed eruption.

In
some cases it can cause pain, bone plate expansion, tooth displacement,
lip numbness and swelling (7). Some patients with erupted odontomas
have reported pain on account of infection in deeply impacted third
molars (8).

On a radiography, these
lesions appear radiopaque, well-defined, denser than bone and
surrounded by a radiolucent rim representing the connective tissue of
the dental follicle. As these elements go through several calcification
stages, their appearance through imaging techniques depends on their
stage of development. CpOD appear as unilocular lesions that may have
multiple tooth-like structures known as denticles. CxOD are solid
radiopaque, sometimes papilliform masses, surrounded by a thin
radiolucent layer that separates them from the surrounding bone (2, 4,
5).

Histollogically, CpOD have a fibrous
capsule of connective tissue which surrounds denticles, formed by pulp
tissue, surrounded by primary or immature dentin, partially
demineralized enamel and primary cementum.

CxOD
have an external capsule of fibrous connective tissue, and the
calcified tissue is formed mainly by primary or immature dentin, enamel
with different degrees of calcification and immature cementum (9, 10).

The
etiology of odontomas is not clear, and various theories have been
suggested: local trauma during primary dentition, inflammatory and
infectious processes, hereditary anomalies and alteration in genetic
components responsible for tooth development (11).

Hitchin
(1971) suggests that odontomas are inherited through the mutation of a
gene in charge of tooth development, possibly after birth. The dental
lamina that gives rise to dental germs usually disappears after
fulfilling its function. However, some of it might remain, known as
rests of Serres. These rests may have a major role in odontoma
etiology, as both CpOD and CxOD might appear where a tooth should be. A
mutation in the epithelial cells that form dental lamina or germ rests
may change the capacity of odontogenic epithelium to go through the cap
and bell stages necessary for tooth formation and yet retain its
ability to stimulate the mesenchymal differentiation necessary for
dentin formation and to form functional ameloblasts and odontoblasts,
which leads to the formation of an odontoma (12).

Clinical case

Male
22-year old patient that attends the Oral and Maxillofacial Surgery
Clinic I at the School of Dentistry of the Universidad de la República
Oriental del Uruguay on account of a swelling on the mandible affecting
teeth 36 to 38. No relevant medical or family history.

Upon
clinical examination, a swelling was detected. It deformed both
mandibular cortical bones, exposing a yellowish hard matter, with an
irregular surface and which resembled dentin tissue. There were no pain
or infection symptoms (Fig. 1).

Fig. 1 – Irregular mass deforming both mandibular cortical bones

The
panoramic radiograph showed a 3.6 cm x 3 cm compact radiopaque mass
surrounded by a thin radiolucent area. The first left lower molar was
retained underneath the mineralized mass. Upper molars were in contact
with the mass (Fig. 2)

The
surgery was performed intraorally under local anesthesia: the lesion
was removed and the first retained molar preserved to allow for
eruption.

Upon histopathological
examination, we detected enamel, dentin and pulp matrix: an erupted
complex odontoma according to its clinical-pathological features
(Fig. 3).

Fig. 3 – enamel, dentin and pulp matrix A: HE 40 and B: HE 100X

A
panoramic radiograph was taken after 2 years to follow up on the
patient. It showed good bone repair and the first left lower molar in
advanced eruption (Fig. 4).

Fig. 4 – Control panoramic radiograph

Discussion

The
WHO classifies odontomas as benign mixed odontogenic tumors. Given
their behavior, they are considered hamartomatous lesions arising from
dental tissues (2). Their frequency varies depending on the report:
between 22 % and 67 % of odontogenic tumors (3, 13, 15). They account
for 30 % of odontogenic tumors in the Anatomic Pathology Department of
the School of Dentistry, Universidad de la República, Uruguay.

Clinically, odontomas can be classified into central (intraosseous), peripheral (extraosseous), and erupted (6).

Erupted
odontomas are intraosseous lesions that appear in the oral cavity. Most
are connected with a retained tooth, usually a second molar. This is
why some authors suggest that the eruptive force of these teeth may
impact odontoma eruption (6).

It is
actually inaccurate to say that there is odontoma eruption, as the
process seems to be different from tooth eruption. This is due to the
lack of periodontal ligament and root. The strength necessary to remove
an odontoma is not connected to fibroblast contractility as is the case
with teeth. Although an odontoma has no root, its increasing size might
lead to pressure-related resorption of the overlying bone and to its
exposure. Odontoma eruption in the oral cavity might also be explained
by bone remodeling in an edentulous area: the bone decreases in height
until the odontoma is exposed (13).

Erupted
odontomas are rare lesions: the first case was reported in 1980 by
Rumel et al. (14). In their 2005 literature review, Junquera et al. (6)
cite an average age of 20.3 years, with a 9 to 59 range. Most odontomas
appeared in the maxilla and were complex. Serra-Serra et al., 2009 (13)
present a review of 20 cases of erupted odontoma. The average patient
age was 25.35 years; most appeared in women and were of the complex
type.

Although
the papers reviewed (Table 1) do no report all the
clinical-pathological data, it is reported that 59.25 % of erupted
odontomas appear in the mandible, between the ages of 8 and 27, the
average age being 17.6, there being no significant sex predilection.
Histologically, complex odontomas are most frequent: 42.4 % of erupted
odontomas.

In our cases, of 107
odontomas, 1.8 % were erupted odontomas (n 2), the average patient age
was 15, one female with a compound odontoma on the maxilla, and one
male with a complex odontoma on the mandible.

In
this report we discuss the case of a male 22-year-old patient, with a
complex erupted odontoma on the mandible, over the first retained
molar. No symptoms were reported.

The
lesion was removed and the impacted tooth preserved. This required the
clinical and radiographic follow-up of the patient for at least a year.
If there are no changes in tooth position, the tooth is surgically
exposed and orthodontic traction is performed. Extraction is
recommended when the retained tooth is ectopic or heterotopic, with
morphological alterations, or when it presents cystic lesions (13, 23).
In this case the odontoma was removed, which allowed the molar to erupt
normally.

Conclusions

Odontomas
are the most frequent benign lesions, and they rarely erupt into the
oral cavity. Erupted odontomas are mainly complex, appear later in life
than other odontomas, and are usually linked to impacted teeth. They
might present pain, inflammation and infection.

The
treatment selected was surgical removal with tooth preservation to
facilitate its eruption, which might be spontaneous or favored by
surgical exposure and orthodontic traction.

Acnowledgements

To
Dr. Pablo Scarrone, Surgeon at the Surgical Department I, School of
Dentistry of the Universidad de la República, Uruguay, for providing
the clinical data on the case presented.